The glucose sensitivity achieved with copper(II) oxide particles with three different morphologies (spheres, platelets, and needles) for application in nonenzymatic glucose sensors was investigated. The morphologies of CuO nanoparticles were controlled by different synthesis parameters, including changes in precipitators of Cu(II) ions, pH values, calcination protocol, and the addition of surfactant and hydrogen peroxide. The role of copper(II) oxide particle morphology in nonenzymatic glucose sensing was studied. The primary driving factor in the electrocatalytic process was investigated for several morphological properties of the material. We studied the effects of exposed crystal faces, specific surface area, pore volume, and grain size of copper oxides on glucose sensitivity. This study showed that the electrocatalytic performance in glucose sensing correlates primarily with the grain size of copper oxide nanoparticles and the capacitance introduced therefrom. The needle-shaped CuO nanoparticles presented the optimal morphology in this application, resulting in good sensitivity to glucose (2.05 mA·mM–1·cm–2), a linear range of 0.05–5 mM glucose, and the best long-term stability among these materials. This work provides insight into the potential use of CuO-based materials in biosensors and into the major contributing factors of metal oxide-based nanoparticles in sensing applications.

Mesoporous silica is often employed as a coating material in core–shell nanoparticles to decrease the possibility of sintering or aggregation of the core particles. In this work, we discovered a surprising morphological transformation during the sulfidation and regeneration (oxidation) of core–shell CuO@mSiO2 materials designed for H2S capture. Although CuS cores were still encapsulated within the silica shells after in situ sulfidation, hollow silica shells formed during the regeneration step as CuO leached out of the shell and aggregated into larger particles. The successful sulfidation of pristine CuO@mSiO2 was facilitated by the restraining effect of silica shells on lattice growth from CuO into CuS, and the mesopores allowed for volume expansion. The phase and morphology changes during the regeneration (oxidation) process leading to the hollow shells were investigated by X-ray diffraction and transmission electron microscopy. It was observed that the cores remained encaged during the disproportionation of CuS to Cu2S, which is the first step in the oxidation of CuS. However, voids were generated when Cu2S was oxidized and reacted with water generated from the condensation of silica. A possible mechanism for this transformation involves the outward diffusion of copper ions through the mesoporous silica, leading to the migration of core particles. This migration was further accelerated by the elevated temperature in the regeneration process and promoted by the formation of the copper sulfate hydroxide through the reaction with water. This work provides key insights into the chemical stability of such core–shell structures under the influence of diffusion-driven structural transformations.

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